Production of ethanol from cheese whey has traditionally been conducted using a yeast belonging to Kluyveromyces sp., e.g. Kluyveromyces fragilis or Kluyveromyces marxianus, since these fermenting organisms can directly ferment lactose to ethanol. However, these yeast suffer from the drawback that they are ethanol sensitive and therefore only processes applying low substrate concentrations and corresponding low ethanol yields have been feasible.
An alternative to using Kluyveromyces sp. as the fermenting organism is to use Saccharomyces cerevisiae. To make this possible the addition of enzymes, like e.g. a beta-galactosidase, is necessary in order to convert the lactose to fermentable sugars. Mehaia and Cheryan (Bioprocess Engineering 5 (1990), 57-61), describes the production of ethanol from hydrolysed whey permeate using Saccharomyces cerevisiae and a beta-galactosidase. In this study the authors obtained an ethanol yield of 0.49 using 10% dry solids in an SSF process. Because of a high beta-galactosidase concentration conversion of 90% of the lactose was completed in less than one hour.
In SSF hydrolysis/saccharification of lactose is carried out simultaneous with the fermentation and the lactase needs to have sufficient at the pH where the SSF is carried out, typically at a pH between 4.0 and 5.0.
It is the purpose of the present invention to improve ethanol yield of the above S. cerevisiae based simultaneous saccharification and fermentation process.